Women will continue on assigned antiretroviral therapy postpartum and will have 11 postpartum clinic visits over a period of 2 years. Blood samples from women will be evaluated for safety and for virologic, pharmacokinetic, and metabolic studies. The first 12 women randomized to Group A will undergo a 4-hour pharmacokinetic profile at 32 to 36 weeks gestation and at 8 weeks postpartum to determine the timing of the nelfinavir trough. The first 20 women randomized to Group B will undergo an 8-hour pharmacokinetic profile at either 16 to 24 weeks or 32 to 36 weeks gestation and then again at 8 weeks postpartum to characterize pharmacokinetics of nevirapine at steady state in pregnancy and in the postpartum period.